I think that the sudden on slaught of all around boats is due to the public wanting a boat that can do it all. The average paddler just wants a kayak that will be comfortable and stable. The all around boat will give them exactly that. The average paddler (which is a BIG percentage of paddlers) doesn't care to have a boat that is going to get them down the knar or a boat that loops the biggest. I am glad to see kayak manufacturers smarten up and realize this! It's a prime example of why the "old" Riot company didn't really sell that many boats. Coran always designed and still does design boats that are all the raddest play machines out there...the problem with this is the average paddler gets there butt kicked in this type of design. Another example is the Space Cadet...great playboat...but average paddlers got their asses kicked!
As far as these all around boats getting down "the gnar" that becomes a personal choice. I creek in the Diesel 75...it got me down Lake Creek, Vallecito, etc. I paddled the Diesel 65 down Lower Meadow and it worked but it was a little bit to slow to resurface and a little squirrely(sP?) It wasn't the boats fault for this...it was my fault for being in a boat I was to heavy for. The point I am trying to make here is that if you are thinking of running some big stuff buy a boat that has plenty of volume. Maybe it's just my preference but I prefer to have a whole lot of boat when I am running something steep.
All in all- it's just what you prefer! The old school Riot boys(Jed Selby, Andre spino-Smith, Daniel Delavernge, etc) used to run USB, Vallecito, Lake Creek in their 007's. It worked and they made it down everything...just watch Buck Fever!